The fish species pool in Europe’s natural lakes is mainly determined by natural colonization processes after the last ice age, while anthropogenic fish introductions further impact the fish species pool. Fish community composition in lakes is then driven by lakes’ trophic state, lake morphology, habitat quality and quantity and biotic interactions. Besides natural lakes, young gravel pit lakes can represent the major water body type in formerly dry landscapes. These lakes originate from anthropogenic excavation processes and are mostly isolated with limited littoral zones. Although they are common, the mechanisms driving gravel pit lake fish communities are rather unknown. In the first part of my thesis, I studied the effects of lake genesis and fisheries management on fish species richness and community composition in small lakes. I used fish communities in unmanaged natural lakes as reference and compared them to unmanaged gravel pit lakes as well as managed gravel pit and natural lakes. In the second part, I investigated the recruitment of littoral deadwood in gravel pit lakes and analysed the importance of deadwood and other littoral structures on littoral fish abundance in gravel pit lakes compared to the lake environmental variables such as nutrient level and lake morphology. I further analysed habitat-specific effects on species-specific littoral fish abundance and focussed explicitly on the effects of deadwood bundles implemented in the littoral zone. I found fisheries management to increase the number of fish species in gravel pit and natural lakes, but not leading to different fish community compositions compared to unmanaged natural lakes. By contrast, unmanaged gravel pit lakes were characterized by a lack of typical lake fish species and a high variation in fish community composition among lakes (β-diversity). I detected littoral deadwood densities in gravel pit lakes to be mainly driven by lake age, riparian tree density in interaction with wind direction and littoral slope in angler-managed lakes, with lowest deadwood densities in shallow areas of angler-managed lakes. Furthermore, deadwood densities were lower in young gravel pit lakes compared to old natural lakes. I detected littoral structures, such as littoral deadwood, as important descriptors of the species-specific, littoral fish abundance in gravel pit lakes with generally positive effects of structure extension on fish abundance. Littoral habitat characteristics were mostly of similar, or even higher, importance for fish abundance compared to lake environmental factors. The implemented deadwood bundles served as appropriate habitats for typical lake fish species in all seasons, especially in winter and attracted on average larger piscivorous fish species. Overall, my findings suggest that fisheries management speeds up the colonization time of fishes in gravel pit lakes leading to species-rich fish communities. Fish community composition is then impacted by classical lake variables describing productivity as well as littoral habitats with species-specific littoral fish abundance being strongly driven by the quality and quantity of littoral structure. The generally low densities of littoral deadwood can be counteracted by implementing deadwood bundles, which serve as appropriate habitats for typical lake fish species, especially in winter.
Fish communities in gravel pit lakes: The impact of fisheries management and littoral structures
Publications , PhD thesis
Matern, S. 2023. Fish communities in gravel pit lakes: The impact of fisheries management and littoral structures. Lebenswissenschaftliche Fakultät der Humboldt Universität zu Berlin.
Appeared in : Lebenswissenschaftliche Fakultät der Humboldt Universität zu Berlin